Transaction Reference Field unique check

We have requirement where we have a manual transaction source. If there is an invoice entered with this source, the reference field will be populated with the Invoice number from customer's system. We want to have a duplicate check on the reference field similar to the duplicate check in Order Management on the Sales Order form. If the purchase order entered for that customer is a duplicate, then the system throws up an error. Is it possible to have similar functionality on AR invoice transaction screen for reference field?